The injection molding industry relies heavily on mold release agents to assure that the product can be readily removed from the mold. The release agent must have a low surface tension. Consequently, fluorinated, siloxane, or wax based compounds are typically employed. In addition to the low surface tension, other factors that contribute to a beneficial mold release are the ease of application and cure. Mold release agents are applied by a variety of methods including spraying, wiping, brushing, and flow coating. Some require a thermal cycle to fully cure the release agent, while others rely on solvent evaporation and/or ambient cure. Long-lasting mold release agents that are solvent-free, and fast-curing, are especially desirable in light of the need for more environmentally friendly products, and the time constraints bearing on many applications.
Existing mold release agents include paraffin, hydrocarbon and carnauba waxes; fluorinated polymers such as tetrafluoroethylene oligomers, hexafluoropropylene oligomers, and derivatives thereof; and triethyl[(perfluorodecyloxy)benzyl]ammonium bromide. Although the waxes are effective mold release agents, several coats must be applied before the mold can be used. Additionally, waxes generally must be reapplied after every use. Furthermore, each of the other foregoing mold release agents provide very few mold release cycles before the mold must be recoated. For example, triethyl[(perfluorodecyloxy)benzyl]ammonium bromide provides only about 3 to 5 mold release cycles, and straight-chain fluorinated surfactants provide only about 1 to 2 mold release cycles.
Silicone release coatings are used to render surfaces non-adherent to materials which would normally adhere thereto, and are widely used as coatings which release pressure-sensitive adhesives for labels, decorative laminates, transfer tapes, and the like. Such release coatings are advantageously formed by the cross-linking of epoxy functional polydiorganosiloxane silicone fluids in the presence of an ultraviolet (UV) cationic initiator. Suitable bis(aryl)iodonium salt cationic photocatalysts, for example bis(4-alkylphenyl)iodonium hexafluoroantimonate, have been disclosed in U.S. Pat. No. 4,279,717 to Eckberg et al., which is incorporated by reference herein. Another class of UV-sensitive catalyst is disclosed in U.S. Pat. No. 5,340,898 to Cavezzan et al., comprising tetrakis(perfluorophenyl) borate anions.
There remains a need for silicone release coating systems which provide faster, more efficient photocatalyzed curing of reactive epoxy functional silicones. U.S. Pat. No. 5,583,195 to Eckberg has reported synthesis and use of epoxy functional silicone polymers which have been partially or completely functionalized by a fluorescing, or a photosensitizing, or a simultaneously fluorescing and photosensitizing substituent bonded to the silicone polymer. These epoxy functionalized silicone derivatives are particularly useful for providing fluorescent dye marking compounds for determining the quality of the release coatings made therewith. In particular, Eckberg discloses reaction of an agent such as anthracene-9-carboxylate with an epoxy silicone to yield a functionalized epoxy silicone that possesses ultraviolet fluorescence activity and photosensitization activity. Such compounds are sensitizers for iodonium photocatalysts, promoting enhanced iodonium miscibility and enhanced photo cure response. Anthracenes however are expensive and therefore impractical for commercial use. Accordingly, there remains a continuing need in the art for commercially viable methods for the derivatization of epoxysilicones which will yield compounds of higher reactivity and excellent adhesion release coating properties.
U.S. Pat. No. 6,232,362 to Agars et al. teaches cycloaliphatic epoxide functionalized polydimethylsiloxane (CEF-PDMS) mold release agents that are UV photocurable. The photosensitized silicones are prepared via the reaction of a photosensitizing molecule containing at least one acid functionality or one convertible to an acid functionality with an epoxysilicone via an acid catalyzed oxirane ring opening reaction. This is achieved using a photosensitizing naphthalene substituent.